Vacuum plasma generators are used, for example, in semiconductor production for coating and etching. Semiconductor production processes may require a radio-frequency (RF) power in the range from 1 to 30 MHz and a power of several kW. Plasma loads, i.e., plasma processes in a vacuum chamber, are highly dynamic and tend to cause arcing, which causes mismatching and hence reflections in RF applications.
Most vacuum plasma generators include at least one amplifier for generating a high-energy RF signal. In the case of mismatching, the energy is reflected by the load. Part (usually a very small part) of the reflected energy is absorbed in the amplifier of the vacuum plasma generator and converted into heat. Much of the energy can be reflected by the amplifier, thus producing multiple reflections and thereby standing waves. This can produce very large amounts of energy that oscillates between the amplifier and the plasma load and can cause damage both to the plasma load and to the amplifier.
U.S. Pat. No. 6,703,080 B2 discloses a vacuum plasma generator that can be connected to a switching power supply and is connected to a driver stage. The driver stage supplies an RF signal to an amplifier stage, where the RF signal is initially divided onto several paths, is subsequently amplified in the paths, and is finally coupled again in a 3 dB coupler to form an amplified RF signal. An insulating stage having a circulator is provided to decouple the amplifier stage from the load impedance changes.
Vacuum plasma generators should have a size that enables them to be mounted close to the vacuum chambers to avoid the need for long expensive cables.
Moreover, in semiconductor production, vacuum plasma generators additionally meet clean room requirements. Forced air exchange between the inside of the generators and the ambient air using ventilators is not desired. Vacuum plasma generators are often designed to be used in different countries having different mains voltages and frequencies. They are mainly used in industry where they must meet high demands as regards interference resistance, wherein at the same time high interference voltages are mostly present in the current supply networks and at the load.